CA1068639A - Trivalent chromium plating baths - Google Patents
Trivalent chromium plating bathsInfo
- Publication number
- CA1068639A CA1068639A CA248,761A CA248761A CA1068639A CA 1068639 A CA1068639 A CA 1068639A CA 248761 A CA248761 A CA 248761A CA 1068639 A CA1068639 A CA 1068639A
- Authority
- CA
- Canada
- Prior art keywords
- ions
- trivalent chromium
- concentration
- plating solution
- sulphate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 title claims abstract description 59
- 229910052804 chromium Inorganic materials 0.000 title claims abstract description 58
- 239000011651 chromium Substances 0.000 title claims abstract description 58
- 238000007747 plating Methods 0.000 title claims abstract description 45
- 229910021653 sulphate ion Inorganic materials 0.000 claims abstract description 52
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims abstract description 43
- -1 sulphate ions Chemical class 0.000 claims abstract description 35
- 239000008139 complexing agent Substances 0.000 claims abstract description 28
- 229910001430 chromium ion Inorganic materials 0.000 claims abstract description 27
- 239000000203 mixture Substances 0.000 claims abstract description 9
- 229910052736 halogen Inorganic materials 0.000 claims abstract description 4
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 35
- 239000000243 solution Substances 0.000 claims description 32
- DHMQDGOQFOQNFH-UHFFFAOYSA-N Glycine Chemical compound NCC(O)=O DHMQDGOQFOQNFH-UHFFFAOYSA-N 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 13
- 239000000758 substrate Substances 0.000 claims description 11
- 239000004471 Glycine Substances 0.000 claims description 10
- 150000002500 ions Chemical class 0.000 claims description 10
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 claims description 9
- 239000004327 boric acid Substances 0.000 claims description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- 239000008151 electrolyte solution Substances 0.000 claims description 3
- 229910021563 chromium fluoride Inorganic materials 0.000 claims 1
- 239000003792 electrolyte Substances 0.000 description 44
- 229940037395 electrolytes Drugs 0.000 description 15
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 14
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 12
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 10
- 230000000694 effects Effects 0.000 description 10
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 9
- 239000000463 material Substances 0.000 description 7
- KWSLGOVYXMQPPX-UHFFFAOYSA-N 5-[3-(trifluoromethyl)phenyl]-2h-tetrazole Chemical compound FC(F)(F)C1=CC=CC(C2=NNN=N2)=C1 KWSLGOVYXMQPPX-UHFFFAOYSA-N 0.000 description 6
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 6
- 150000001450 anions Chemical class 0.000 description 6
- 235000013024 sodium fluoride Nutrition 0.000 description 6
- 239000011775 sodium fluoride Substances 0.000 description 6
- 229910001379 sodium hypophosphite Inorganic materials 0.000 description 6
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 5
- 239000003795 chemical substances by application Substances 0.000 description 5
- 238000001816 cooling Methods 0.000 description 5
- 238000010792 warming Methods 0.000 description 5
- 239000002253 acid Substances 0.000 description 4
- 239000000872 buffer Substances 0.000 description 4
- GRWVQDDAKZFPFI-UHFFFAOYSA-H chromium(III) sulfate Chemical compound [Cr+3].[Cr+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O GRWVQDDAKZFPFI-UHFFFAOYSA-H 0.000 description 4
- 235000019270 ammonium chloride Nutrition 0.000 description 3
- 235000015217 chromium(III) sulphate Nutrition 0.000 description 3
- 239000011696 chromium(III) sulphate Substances 0.000 description 3
- 239000000470 constituent Substances 0.000 description 3
- 230000001965 increasing effect Effects 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- LZZYPRNAOMGNLH-UHFFFAOYSA-M Cetrimonium bromide Chemical compound [Br-].CCCCCCCCCCCCCCCC[N+](C)(C)C LZZYPRNAOMGNLH-UHFFFAOYSA-M 0.000 description 2
- 238000007792 addition Methods 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000004070 electrodeposition Methods 0.000 description 2
- 230000002708 enhancing effect Effects 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- ACVYVLVWPXVTIT-UHFFFAOYSA-M phosphinate Chemical compound [O-][PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-M 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000004094 surface-active agent Substances 0.000 description 2
- 101100087530 Caenorhabditis elegans rom-1 gene Proteins 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 241001600451 Chromis Species 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 241000357437 Mola Species 0.000 description 1
- 101100305983 Mus musculus Rom1 gene Proteins 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 150000001844 chromium Chemical class 0.000 description 1
- 230000000536 complexating effect Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 230000003467 diminishing effect Effects 0.000 description 1
- 238000009713 electroplating Methods 0.000 description 1
- KWIUHFFTVRNATP-UHFFFAOYSA-N glycine betaine Chemical compound C[N+](C)(C)CC([O-])=O KWIUHFFTVRNATP-UHFFFAOYSA-N 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- ACVYVLVWPXVTIT-UHFFFAOYSA-N phosphinic acid Chemical compound O[PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-N 0.000 description 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
Landscapes
- Electroplating And Plating Baths Therefor (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An aqueous trivalent chromium plating bath having low temperature stability comprising trivalent chromium ions preferably in a concentration of at least 0.2 M, sulphate ions preferably in a concentration of at least 0.3 M, a weak complexing agent for the chromium ions in a concentration of at least 0.1 M, and halogen ions in a concentration of at least 0.025 M. The halogen ions can be fluoride ions, chloride ions or mixtures thereof.
An aqueous trivalent chromium plating bath having low temperature stability comprising trivalent chromium ions preferably in a concentration of at least 0.2 M, sulphate ions preferably in a concentration of at least 0.3 M, a weak complexing agent for the chromium ions in a concentration of at least 0.1 M, and halogen ions in a concentration of at least 0.025 M. The halogen ions can be fluoride ions, chloride ions or mixtures thereof.
Description
-~; 10~ 35a The present invention relates to trivalent chromium plating baths and in particular to plating baths containing weak complexing agents such as hypopho---phite and glycine.
It is known to electroplate chromium from aqueous baths containing trivalent chromium ions and an organic buffer, preferably an aprotic buffer such as dimethylformamide (DMF). Such techniques are described in British Patent Specification No. 1,114,913. In electroplating from electrolytes buffered with e.g. DMF, it is advantageous to ensuxe, as far possible, that the electrolyte has a single anion, usually sulphate or chloride. It is preferred not to use mixed anion electrolytes (see in this regard British Specification Nos. 1, 194,913 and 1, 333,714). More recently a variety of trivalent chromium electrolytes have been developed which use weak complexing agents instead of or, optionally but not usually preferably, with an organic -buffer. Typical weak complexing agents are hypophosphite, usually as the sodium salt, glycine and mixtures of these. -Such systems are described in U.S. Patent No. 3, 917,517 and British Patent Application No. 38320/74, published as U.K.
Specification No. 1, 488,381. The term "weak complexing ; -agent for trivalent chromium ions" is used and defined herein as meaning a complexing agent for trivalent chromium ions which does not bind trivalent chromium so strongly as to ;~
prevent electrodeposition of chromium from aqueous trivalent chromium solutions containing it.
One advantage of electrolytes using weak complexing agents is that they are more tolerant towards mixed anions than electrolytes using organic buffers such as DMY. However, electrolytes using weak complexing agents based on sulphate ' . ~:
- '. ~L06~3~j39 : ~ ~
as the anion, have a disadvantage in that if the electrolyte is cooled it deteriorates and bath constituents can crystallize out.
Once they have crystallised out these materials are difficult to get back into solution and it may be necessary to heat the electrolyte well above its normal operating temperature to complete re-dissolution. In the laboratory this is a minor inconvenience, but in large scale plant operation such cooling, which can easily occur when the electrolyte is not in use such as overnight or over a weekend, particularly when the weather is cool, can precipitate sufficient material that the delay and expenditure of energy - ~
; necessary to re-dissolve the materials may make such electro-lytes uneconomic to operate despite their other advantages.
It is an object of the present invention to improve the low temperature stability of sulphate based trivalent chromium electrolytes.
Accordingly, the present invention principally provides a trivalent chromium plating solution comprising water, trivalent chromium ions, sulphate ions, a weak complexing agent for said trivalent chromium ions, and halogen ions selected from the group consisting of fluoride~ions, chloride ions and mixtures thereof.
~he present invention in one aspect provides an aqueous trivalent chromium plating bath electrolyte based on sulphate as the anion which comprises trivalent chromium ions in a concentration of at least 0.2 lar, sulphate ions in ;~
a concentration of from 1 to 6 molar, a weak complexing agent for trivalent chromium ions in a concentration of at least 0.1 molar, and chloride ions in a concentration of from 0.1 :
~.068639 to 5.0 molar;the molar ratio of chloride ions to sulphate ions being from 1:60 to 5:1 but preferably being in the range from 1:7 to 5:1.
In another aspect the invention provides a method for electrodepositing chromium on a substrate which comprises immersing said substrate as the cathode in an electrolyte solution comprising water, trivalent chromium ions in a concentration of at least 0.2M, sulphate ions in a concent-ration of at least 0.2M, sulphate ions in a concentration of from 1 to 6M, a weak complexing agent in a concentration of at least O.lM, and chloride ions in a concentration of from O.lM to 5.OM, and passing an electric current through said solution thereby to deposit said trivalent chromium ions on said substrate.
In a preerred embodiment of the plating solution and of the method of using tKe solution there are present both fluoride and chloride ions.
The concentration of trivalent chromium ions above 0.2 molar is typical of trivalent chromium baths but is usually limited to a maximum of 2 molar by the solubility of chromic sulphate. For decorative plating the optimum ~ -concentration is about 1 molar. ;~
'~
:~ , .~ .
.~,~, .
lo68639 ~he concentration of sulphate ions is typical for tri-valent chromium baths and the preferred range is from 2 to 4 molar.
The concentration of chlorlde ions and the molar ratio of chloride ions to sulphate ions are not critical ~o tlle invention. However, less than o.i molar chloride or a lower molar ratio than 1:60 produces no slgnificant efect. ~ concentration of chloride higher than l.5 molar . . ' . , '' ~ .
or a molar ratio higher than i:2.5 produces no further ~
;.;
increase in stability. The use of higher concentrations `~
of chloride does however lead to significant improve-ments in solution conductivity providing a distinct commercial advantage. Concentrations of 2 to 4 molar chloride are therefore preferred.
The concentration and precise nature of the weak complexing agent are not critical to the useful , :
effect of chloride ions in sulphate based electrolytes. -~
Hypophosphite and/or glyclne are the preferred weak complexing agents and will typi~alIy be used at a con- .~
centration of from 0.1 to 6 mola.r and preferably from ~ ~;
0.25 to 3 molar, the uppex limit being largely a -function of solubility.
The eiectrolyte may option~'ly include a variety o other materials such as are typically used in trivalent chromium electrolytes. Thus boric acid can be included as .
a current efficiency enhancing agent at concentrations up to saturation (about 1 molar) and typically at 20-60 gl~l.
Ammonium ions can be added to increase the conductivity of , the bath typically at a concentration, when used, of from 1 to 7 molar and preferably greater than 5 molar for optimum effect. Conveniently the ammonium ion or a part , ~' , . . _~ .. ..... .. ~
~ 06~3~39 ~f it can be added as ammonium chloride, thus also acting as the source of chloride ions. Larger concentrations of ammonium ions will usually be added as sulphate or as ammonia and free acid. The electrolyte may also include one or more surface active agents such as cetyl trimethyl-ammonium bromide in concentrations up to 50 ppm. Such additives are normal in trivalent chromi~lm electrolytes. l`
The baths o~ the in~ention typically operate at temperatures from amblent temperature to 50C and preferably from 25 to 35C.
Th~ additions of chloride ions to tri~alent . .
ch~omium sulphate baths has the effect of increasing the low temperature solubility of the less soluble ;
bath constituents. Indeed, addition of a suitable quantity of chloxide ion to a bath which already has a precipitate in it can greatly ease re-dissoluLion ` -of the precipitated constituents to more xeadily . : .
establish the complexed state most suitable for plating.
If a sulphate bath containing chloride develops a pre- ~
cipitate on cooling then simply re-warming to its normal ~ ;
~` operating tem~erature can suffice to re-dissolve the ~ precipitated material ir a rorm s~itabie for eiectro- - -`' reduction.
~; A further advantage of.adding or including -~
chloride ions in trivalent chromium sulphate baths is -that the overall current and practical plating range , efficiency of electrodeposition is improved signifi-;: .:
cantly. With optimum ele~trolytes the current - , . . . .
efficiency of mixed chloride/sulphate trivalent chromium electrolytes can be as high as 170~ of that of a similar bath omitting the chloride. The plating range of an optimised chloridejsulphate bath is typically from 30 to 104 Am~2. However, in commercial plant operation the range is somewhat narrower and is typica]ly 70 to 104 ~m 2, .. . .
.
~6~3639 ~ ~
The present lnvention in another aspect provides an aqeuous trivalent chromium plating bath electrolyte based on sulphate as anion which comprises:
.
Trivalent chromium ions in a concentration of at least 0.2 molar, sulphate ions in a concentration of at least 0.3 molar, a weak cGmplexing agent for txivalent chromium ions in a concentration of at least 0.1 molar, and luoride ions in a concentration of at least 0.025 molar. ~
- ~he concentrati-on of trivalènt chromium ions above .: , , ~ ;
0.2 molar is typical of trivalent chromium baths but is nsually limited to a maximum of 2 molar by the solubility o~ chromic sulphate. For decorative plating the optimum concentration is about 1 molar.
;. :":
~ The minimum concentration of sulphate ions given i , is a practical minimum figure corresponding to the minimum ~ level of trivalent chromium. The pre~erred range is from ; 1 to G molar optimally from 2 to 4 molar., .~ , . - - - .~ .
The particular concentration and precise natu~e of the weak complexing agent are not critical to the useful ;
effect of fluoride ions in sulphate ~ased electrolytes.
~ Hypophosphitè and/or glycine are the preferred weak com- ' ;
; ~ plexing agents and will typicalIy be used at a concentra- ~ -tion of from 0~1 to 6 molar pre~erably 0.25 to 3 molar, . , , the upper limit being largely a function of solubility.
Glycine is additionally advantageous, because the chromium deposit usually has a lighter color.
The concentration of fluori~e must be at least 0.025 molar in order to obtain any appreciable effect.
The maximum concentration is limited by solubility and diminishing returns to 1.5 molar. Preferably the concen-.: 6 , - , . :.. ,-: . . . . .
; , . . ~ . "
. . . . . ..
~(:)6~363~ `
. ~:
~ration is up to 1.25 molar, optLmally from 0.1 to 0.7 molar. ConvenientlY the fluoride can be added as sodium fluoride and the minimum level corresponds to about l gl~
of NaF and the optimum from about 5 to 25 gl~l. Other ~}uoride containing salts and materials can be used as ~luoride ion sources, In order to ensure a relatively high electrolyte conductivity it is preferred to include ammonium ion in the electrolyte. When used the concentration of ammonium ;
~inn will typically be ~rom 1 to 7 molar and preferably greater than 5 M for optimum effect. The ammonium ion can conveniently be added as the sulphate (but see below concerning mixed sulphate/chloride systems). The electro-lyte may optionally include a variety of other materials such as are typically used in trivalent chromium electrolytes.
~., For example, boric acid can bé included~as a current effi- ;-.
ciency enhancing agent at concentrations up to saturation (about 1 molar) typicaIly at 20 to 60 gl~l. The electrolyte ~-may also include one or more surface active agents such as cetyltrimethylammonium bromide in concentrations up to 50 :. .. .
ppm. Such additives are normal in trivalent chromium electrolytes.
The effect of adding fluoride to chromic sulphate baths is to impair the production of particles of difficultly electroreducible chromium complexes which tend to form at low tsmperature. Fluoride ion has the ability to break up those , -- `
moieties enabling the optimum equilibrium to be established ^ ~
more readily. The baths of the invention typically operate ~-~t tsmperatures from ambient temperature to 50~C and pre-ferabiy from 25 to 35~iC. Restarting ~lating then only -requires warming to operating temperature - extensive ~-' '.. `,: " ' '.:
; - 7 --- ~068639 warming a~ elevated temperatures being unnecessary. In similar baths not containing fluoride it would probably be necessary to heat the bath at a relatively high temperature, typically 50C or higher, for a prolonged period to achieve dissolution of the precipitate.
A further effect of fluoride in that it acts as a platin~ exhaltant. The average plating eficiency o a ~luoride containing, sulphate based trivalent chromium `
plating bath can be double that of a similar bath without ;-the fluoride. A further advantage is that the colour of the chromium deposited, which in trivalént chromium systems `
tends to be rather dar~,is lighter when deposited in the presence o~ fluoride and more nearly matches the color of plate produced from hexavalent chromium plating baths.
.. .... ~ - - .
As is indicated above fluoride ion can be included in mixed sulphate/chloride baths. The inclusion of chloride in sulphate trivalent chromium baths is itself, advantageous, but the effect of chloride on its own is less than the effect . ~ . . . .
of fluoride. The concentration of chloride ion, when present, ;~
will usuall~ be in th range 0.1 to 5 molar preferably 0.5 ~-to 5 molar. The molar ratio of chloride to sulphate in such baths should be in the range 1:60 to 5:1. The chloride ~ ion can conveniently be added as ammonium chloride.
.' . :
The plating range of an optimised fluoride containing sulphate based bath is typically from 30 to 10~ Am~2. However - in commercial plant operations the range is somewhat narrower ` and is typically 50 to 104 Am . Thus, fluoride acts to reduce the loss of efficiency of: sulphate based baths at low .,.
current densities. Because of the increased efficiency given to trivalent chromium plating baths the average rate of plating .-. ~ .
; 8 ~
... . . .
~?6~363~
.~ ' ' - .
.,.
from baths of the invention can be as high as 0.15 ~m min 1. Higher rates of deposition can be achieved by raising the temperature or reducing the pH.
In addition to the electrolyte described above the invention also includes a method of elec~roplating comprising providing an anode and a cathode in an electrolyte of the invention and passing an electric current through the electro-lyte whereby chromium is electrodeposited on the cathode.
The method of the invention can be carried out at a pH of from 0.5 to 7. However, in order to maintain a wide plating range-the preferred pH is from 1.5 to 4. The make-up pH of an electrolyte comprising the necessary components as a solution of the stoichiometrically neutral salts in water is usually within this range. However the pH can be readily adjusted by adding suitable small quantities of ~ acid or alkali as necessary.
-~ :
The electrolyte may be made up as in British Specification No. 1, 488,381, by a PH changing technique which can ensure formation of the desired complex between the trivalent chromium and the weak complexing agent.
!
The anodes used in the process of the invention are not critical to the process of the invention. Carbon anodes will .~ i , ~ in general be used because of their cheapness and convenience.
;'- The following Examples illustrate the invention:
, EXAMPLE 1 .; . . .
' An aqueous electrolyte having the following composition was made up:
1 M trivalent chromlum as sulphate 4 M NH4 as sulphate 0.75 M Boric Acid 1 M Sodium hypophosphite `'~
_ g_ 68t;3.9 .
Using a portion of the electrolyte a Hull Cell panel was plated under.the following conditions~
pH .- 3.1 .:
: Temperature 25C
S Hull Cell current lOA . .. . . .:
~ull Cell voltage 14V
The rësults of plating for 60 seconds were: ..
Current Density Am-2 500 1000 2000 3500 5000 -~ :
~Thick~es.s.~m 0......... 10 Ø. 11 0.1.0 0.... 11 0... 12 ~ ~
. . . , , ,,`: .
.: 10 A further portion of the electrolyte was cooled :
.. : . .. , . , ": ..
` to 10C for 12 hours and re-warmed to 25DC. A Hull Cell :. . : .
-; panel was plated under the same conditions as used above. . .
The results of plating for 60 seconds were~
.` Current.Density Am-2 500 1000 2000 3500 5000 :
lS . Thickness ~m 0.09 0.05 0.05 0.07 0.10 `~
., `~ ~s can be seen a considerable loss in plating -.
.~. : Speed occurred.
.. : , -. . .
An aqueous electrolyte having the following 20compos:ition~was made up: , ~ :
~ 1 M trivalent chromiu~ as suiphate ~.
;~ 3 M NH4~ as sulphate ::
1 M NH4~ as chloride ~;~ . 0.75 M ~oric acid 1 ~ Sodium hypophosphite . ~
' ~
.~ .
. : ' '; ~
.
.~ .
. ' .
~ . , : :, . . .. . j.... .
~068~;~9 . The electrolyte was divided into two portions : ~
and Hull Cell panels were plated-a~ set out in Example 1. :
~::
The results were: . , . .. ::;
' , .,, , ' . ' . , '`'~' '~ ',' .
Without cooling: :~
Current Density Am ~ 500 1000 2000 3500 5000 .. .
Thickness ~m 0.15 0.16 0.16 0.16 0.17 .
:, After cooling and re-warming: ~
Cuxrent Density Am~2 500 1000 2000 3500 5000 ::
. Thickness ~m 0.13 0.15 0.15- 0;15 0.15 ~: :
10 . ThP loss in plating speed after cooling and re~warming is . ~ .
. vixtually negligible. . . :.
.. ,. ., - ',' '- ~.
EX~lPLE 3 Ex~.ples l and 2 were repeated ~ut using glycine:~
, ,~... .
.. as the weak complexing agent. The observed efect of .
. 15 including chloride ion in the electrolyte was similar to .
that observed in Example 2.
~, . . .... -~ ...
` . EXA~LE 4 .
An aqueous electrolyte having the following compo~
sition was made up: . . ~. .................. .. ~. : .
... . .
1 M trivalent chromium as sulphate .~: :
3 M NH4f as sulphate . 3 M NH4~ as chloride 0.75 M Boric acid : . .. . : ..
. 1 M sodium hypophosphite ~.`
. . .
: 25 The performance of this electrolyte ~as identical to : -th~t of Example 2 except the ~lull Cell was in this case 11 volts , '"' . , -' ' , ' '. :''.
, !. ~ , - 11 - ,'. -.:,, '' . '' ''' 1061~63~
as compared to 13 volts for Example 2 indicating a ~`
superior conductivity in presence o~ higher chloride ion and ammonium ion contents.
. ':.' .
'' ' ~
EXAMPLE
An aqueous electrolyte was made up having the following composition~
1 molar trivalent chromium (as sulphate) 4 molar NH4~ (as sulphate) l molar boric acid ~:
1 molar sodium hypophosphite A Hull Cell panel was plated for 60 seconds under ,, thè following conditions: -p~ .3.0 Hull Cell current lOA
Temperature 25C Hull Cell voltage 16V `' .
The results were as follows:
/ Curxent Density (Am~2) 300 ;600 1~00 3000 5000.
`A . Thickness (~m~ 0.06 0.08 0.07 0.08 0.06 .:20 ~- .
~ EXAMPLE 6 .~ ~ Example 5 was repeated exc~pt that 6 M NH4~ ion ;~ was provided as a mixture of the sulphate t3 Mj and the . . . ~ .
chloride ~3 M). The Hull Cell panel results were: .
Current Density (Am-2) 300 500 1000 2500 5000 ; .. :.
ThicXness (~m~ 0.07 0.08 0.09 0.10 0.10 ~
- '.~
,. . ~' - ~.
~ 12 --Q76~63g ~ ; ~
-. . ~MPLE 7 ~
Example 5 was répeated except that 20 g~
(ca 0.5 M) sodium fluoride was included in the electrolyte. :`
The Hull Cell panel results were~
Current Density (Am 2) 300 500 1000 2500 5000 ~ .
Thickness (~m) 0.710 0.14 0.14.. 0.13 0.15 . There was a marked exhaltation of plating rate in .
.the presence of the fluoride.
:., .. . ' ~. ' ExAMpLE 8 Example 6 was repeated except that 20 gl~l NaF . ~
`; was included in the electrolyte. The Hull Cell panel results were: , :
Current Density (Am-2) 300 600 1000 3000 5000 .
. :
Thickness ~m) 0.12 0.14 0.15 0.14 0.14 : . Again there was a significant improvement in :
plating rate. .................................................... ~. :;.
~n a~ueous electrolyte was made up having the ollo~ing composition~
I Molar trivalent chromium (as sulphate) ..
4 ~olar NH4~ (as sulphate) `; ~ :
~.~ 1 Molax boric acid .-.
''. 7 1 Molar ~lycine ~,, ;
;~ A Elull Cell panel was plated for 60 seconds ~. ~
under the following condltion: : ~ .
p~ 2.8 ~ull Cell current 10A
:. . Temp. 25C Hull Cell voltage 16V
` 30 Th.e results were as follows~
:; Current Density (Am 2) 300 600 1000 2500 4500 ;
. Thickness (~m) 0.02 0.08 0.10 0.14 0016 - 13 - :.
, -, , .: , .,: . .. .
:` 10{;8639 ~ .
. EXAMPLE l~
Example 9 was repeated except that the 4 ~ NH
ion was provided as a mixture of the sulphate ~3 M) and the chloride (1 M) and that 20 gl 1 NaF was included. The results were as follows~
Çurrent Density (Am 2) 300 500 1000 2500 5000 .Thickness (~m) 0.05 0.10 0.11 0.15 0.16 EXAMPLE ll `lO The following aqueous electrolyte was made up: :-: l Molar trivalent chromium (as sulphate) .
3 Molar NH~+ ~as sulphate) --l Molar NH4~ (as chloride) l ~olar ~oric acid 0O5 Molar glycine 0.6 M sodium hypophosphite i;
20 g/l sodium fluoride !
A Hull Cell panel was plated for 60 seconds under the following c~nditions: l, `
. p~ 2.75 . Hull Cell current lOA - :
Temp. 26C Hull Cell voltage lOV.
: ~he results were as follo:rs:
; ' '' ' .:
.
.
;': ' .
:, ~; ~ 106~3639 Current Density (Am 2) 300 sno lO9O 2500 5000 ~ -Thickness (~m) 0.07 0.12 0.12 0.16 0~15 -.. . . . . .
EX~AMPLE 12 .. ... . .
Chromium was plated from a solution comprised `~
of~
Chrome tan 260 g/l .~ ~mmonium sulphate 180 ~
Ammonium chloride 15~ g/l Sodium flua~i~e 15 g~
Boric acid 40 g/l Sodium hypophosphite 100 g/l This solution showed good Hull Cell characteristics ~, ~ and was ultimately shown to work well on the gallon and sixty gallon sc~le~. The color of the chromium dep~sit~was slightly darker than that achieved~with conventional hexavalent chromium ;~
solutions but gave the impression of increased color depth and ~ ;
was~consid~ered to be attractlve.
The throwing power was significàntly improved and ~`
20 ~ high current density burning was substantially eliminated ~ -since the plating~rate was more or less constant regardless of the c~rrent density applied.
: ' ;:: ` i,' . .. . .
. ~
! , :
- ~, -, ' ' ~, , ,'.'. ' r . ~
~ 15 - v
It is known to electroplate chromium from aqueous baths containing trivalent chromium ions and an organic buffer, preferably an aprotic buffer such as dimethylformamide (DMF). Such techniques are described in British Patent Specification No. 1,114,913. In electroplating from electrolytes buffered with e.g. DMF, it is advantageous to ensuxe, as far possible, that the electrolyte has a single anion, usually sulphate or chloride. It is preferred not to use mixed anion electrolytes (see in this regard British Specification Nos. 1, 194,913 and 1, 333,714). More recently a variety of trivalent chromium electrolytes have been developed which use weak complexing agents instead of or, optionally but not usually preferably, with an organic -buffer. Typical weak complexing agents are hypophosphite, usually as the sodium salt, glycine and mixtures of these. -Such systems are described in U.S. Patent No. 3, 917,517 and British Patent Application No. 38320/74, published as U.K.
Specification No. 1, 488,381. The term "weak complexing ; -agent for trivalent chromium ions" is used and defined herein as meaning a complexing agent for trivalent chromium ions which does not bind trivalent chromium so strongly as to ;~
prevent electrodeposition of chromium from aqueous trivalent chromium solutions containing it.
One advantage of electrolytes using weak complexing agents is that they are more tolerant towards mixed anions than electrolytes using organic buffers such as DMY. However, electrolytes using weak complexing agents based on sulphate ' . ~:
- '. ~L06~3~j39 : ~ ~
as the anion, have a disadvantage in that if the electrolyte is cooled it deteriorates and bath constituents can crystallize out.
Once they have crystallised out these materials are difficult to get back into solution and it may be necessary to heat the electrolyte well above its normal operating temperature to complete re-dissolution. In the laboratory this is a minor inconvenience, but in large scale plant operation such cooling, which can easily occur when the electrolyte is not in use such as overnight or over a weekend, particularly when the weather is cool, can precipitate sufficient material that the delay and expenditure of energy - ~
; necessary to re-dissolve the materials may make such electro-lytes uneconomic to operate despite their other advantages.
It is an object of the present invention to improve the low temperature stability of sulphate based trivalent chromium electrolytes.
Accordingly, the present invention principally provides a trivalent chromium plating solution comprising water, trivalent chromium ions, sulphate ions, a weak complexing agent for said trivalent chromium ions, and halogen ions selected from the group consisting of fluoride~ions, chloride ions and mixtures thereof.
~he present invention in one aspect provides an aqueous trivalent chromium plating bath electrolyte based on sulphate as the anion which comprises trivalent chromium ions in a concentration of at least 0.2 lar, sulphate ions in ;~
a concentration of from 1 to 6 molar, a weak complexing agent for trivalent chromium ions in a concentration of at least 0.1 molar, and chloride ions in a concentration of from 0.1 :
~.068639 to 5.0 molar;the molar ratio of chloride ions to sulphate ions being from 1:60 to 5:1 but preferably being in the range from 1:7 to 5:1.
In another aspect the invention provides a method for electrodepositing chromium on a substrate which comprises immersing said substrate as the cathode in an electrolyte solution comprising water, trivalent chromium ions in a concentration of at least 0.2M, sulphate ions in a concent-ration of at least 0.2M, sulphate ions in a concentration of from 1 to 6M, a weak complexing agent in a concentration of at least O.lM, and chloride ions in a concentration of from O.lM to 5.OM, and passing an electric current through said solution thereby to deposit said trivalent chromium ions on said substrate.
In a preerred embodiment of the plating solution and of the method of using tKe solution there are present both fluoride and chloride ions.
The concentration of trivalent chromium ions above 0.2 molar is typical of trivalent chromium baths but is usually limited to a maximum of 2 molar by the solubility of chromic sulphate. For decorative plating the optimum ~ -concentration is about 1 molar. ;~
'~
:~ , .~ .
.~,~, .
lo68639 ~he concentration of sulphate ions is typical for tri-valent chromium baths and the preferred range is from 2 to 4 molar.
The concentration of chlorlde ions and the molar ratio of chloride ions to sulphate ions are not critical ~o tlle invention. However, less than o.i molar chloride or a lower molar ratio than 1:60 produces no slgnificant efect. ~ concentration of chloride higher than l.5 molar . . ' . , '' ~ .
or a molar ratio higher than i:2.5 produces no further ~
;.;
increase in stability. The use of higher concentrations `~
of chloride does however lead to significant improve-ments in solution conductivity providing a distinct commercial advantage. Concentrations of 2 to 4 molar chloride are therefore preferred.
The concentration and precise nature of the weak complexing agent are not critical to the useful , :
effect of chloride ions in sulphate based electrolytes. -~
Hypophosphite and/or glyclne are the preferred weak complexing agents and will typi~alIy be used at a con- .~
centration of from 0.1 to 6 mola.r and preferably from ~ ~;
0.25 to 3 molar, the uppex limit being largely a -function of solubility.
The eiectrolyte may option~'ly include a variety o other materials such as are typically used in trivalent chromium electrolytes. Thus boric acid can be included as .
a current efficiency enhancing agent at concentrations up to saturation (about 1 molar) and typically at 20-60 gl~l.
Ammonium ions can be added to increase the conductivity of , the bath typically at a concentration, when used, of from 1 to 7 molar and preferably greater than 5 molar for optimum effect. Conveniently the ammonium ion or a part , ~' , . . _~ .. ..... .. ~
~ 06~3~39 ~f it can be added as ammonium chloride, thus also acting as the source of chloride ions. Larger concentrations of ammonium ions will usually be added as sulphate or as ammonia and free acid. The electrolyte may also include one or more surface active agents such as cetyl trimethyl-ammonium bromide in concentrations up to 50 ppm. Such additives are normal in trivalent chromi~lm electrolytes. l`
The baths o~ the in~ention typically operate at temperatures from amblent temperature to 50C and preferably from 25 to 35C.
Th~ additions of chloride ions to tri~alent . .
ch~omium sulphate baths has the effect of increasing the low temperature solubility of the less soluble ;
bath constituents. Indeed, addition of a suitable quantity of chloxide ion to a bath which already has a precipitate in it can greatly ease re-dissoluLion ` -of the precipitated constituents to more xeadily . : .
establish the complexed state most suitable for plating.
If a sulphate bath containing chloride develops a pre- ~
cipitate on cooling then simply re-warming to its normal ~ ;
~` operating tem~erature can suffice to re-dissolve the ~ precipitated material ir a rorm s~itabie for eiectro- - -`' reduction.
~; A further advantage of.adding or including -~
chloride ions in trivalent chromium sulphate baths is -that the overall current and practical plating range , efficiency of electrodeposition is improved signifi-;: .:
cantly. With optimum ele~trolytes the current - , . . . .
efficiency of mixed chloride/sulphate trivalent chromium electrolytes can be as high as 170~ of that of a similar bath omitting the chloride. The plating range of an optimised chloridejsulphate bath is typically from 30 to 104 Am~2. However, in commercial plant operation the range is somewhat narrower and is typica]ly 70 to 104 ~m 2, .. . .
.
~6~3639 ~ ~
The present lnvention in another aspect provides an aqeuous trivalent chromium plating bath electrolyte based on sulphate as anion which comprises:
.
Trivalent chromium ions in a concentration of at least 0.2 molar, sulphate ions in a concentration of at least 0.3 molar, a weak cGmplexing agent for txivalent chromium ions in a concentration of at least 0.1 molar, and luoride ions in a concentration of at least 0.025 molar. ~
- ~he concentrati-on of trivalènt chromium ions above .: , , ~ ;
0.2 molar is typical of trivalent chromium baths but is nsually limited to a maximum of 2 molar by the solubility o~ chromic sulphate. For decorative plating the optimum concentration is about 1 molar.
;. :":
~ The minimum concentration of sulphate ions given i , is a practical minimum figure corresponding to the minimum ~ level of trivalent chromium. The pre~erred range is from ; 1 to G molar optimally from 2 to 4 molar., .~ , . - - - .~ .
The particular concentration and precise natu~e of the weak complexing agent are not critical to the useful ;
effect of fluoride ions in sulphate ~ased electrolytes.
~ Hypophosphitè and/or glycine are the preferred weak com- ' ;
; ~ plexing agents and will typicalIy be used at a concentra- ~ -tion of from 0~1 to 6 molar pre~erably 0.25 to 3 molar, . , , the upper limit being largely a function of solubility.
Glycine is additionally advantageous, because the chromium deposit usually has a lighter color.
The concentration of fluori~e must be at least 0.025 molar in order to obtain any appreciable effect.
The maximum concentration is limited by solubility and diminishing returns to 1.5 molar. Preferably the concen-.: 6 , - , . :.. ,-: . . . . .
; , . . ~ . "
. . . . . ..
~(:)6~363~ `
. ~:
~ration is up to 1.25 molar, optLmally from 0.1 to 0.7 molar. ConvenientlY the fluoride can be added as sodium fluoride and the minimum level corresponds to about l gl~
of NaF and the optimum from about 5 to 25 gl~l. Other ~}uoride containing salts and materials can be used as ~luoride ion sources, In order to ensure a relatively high electrolyte conductivity it is preferred to include ammonium ion in the electrolyte. When used the concentration of ammonium ;
~inn will typically be ~rom 1 to 7 molar and preferably greater than 5 M for optimum effect. The ammonium ion can conveniently be added as the sulphate (but see below concerning mixed sulphate/chloride systems). The electro-lyte may optionally include a variety of other materials such as are typically used in trivalent chromium electrolytes.
~., For example, boric acid can bé included~as a current effi- ;-.
ciency enhancing agent at concentrations up to saturation (about 1 molar) typicaIly at 20 to 60 gl~l. The electrolyte ~-may also include one or more surface active agents such as cetyltrimethylammonium bromide in concentrations up to 50 :. .. .
ppm. Such additives are normal in trivalent chromium electrolytes.
The effect of adding fluoride to chromic sulphate baths is to impair the production of particles of difficultly electroreducible chromium complexes which tend to form at low tsmperature. Fluoride ion has the ability to break up those , -- `
moieties enabling the optimum equilibrium to be established ^ ~
more readily. The baths of the invention typically operate ~-~t tsmperatures from ambient temperature to 50~C and pre-ferabiy from 25 to 35~iC. Restarting ~lating then only -requires warming to operating temperature - extensive ~-' '.. `,: " ' '.:
; - 7 --- ~068639 warming a~ elevated temperatures being unnecessary. In similar baths not containing fluoride it would probably be necessary to heat the bath at a relatively high temperature, typically 50C or higher, for a prolonged period to achieve dissolution of the precipitate.
A further effect of fluoride in that it acts as a platin~ exhaltant. The average plating eficiency o a ~luoride containing, sulphate based trivalent chromium `
plating bath can be double that of a similar bath without ;-the fluoride. A further advantage is that the colour of the chromium deposited, which in trivalént chromium systems `
tends to be rather dar~,is lighter when deposited in the presence o~ fluoride and more nearly matches the color of plate produced from hexavalent chromium plating baths.
.. .... ~ - - .
As is indicated above fluoride ion can be included in mixed sulphate/chloride baths. The inclusion of chloride in sulphate trivalent chromium baths is itself, advantageous, but the effect of chloride on its own is less than the effect . ~ . . . .
of fluoride. The concentration of chloride ion, when present, ;~
will usuall~ be in th range 0.1 to 5 molar preferably 0.5 ~-to 5 molar. The molar ratio of chloride to sulphate in such baths should be in the range 1:60 to 5:1. The chloride ~ ion can conveniently be added as ammonium chloride.
.' . :
The plating range of an optimised fluoride containing sulphate based bath is typically from 30 to 10~ Am~2. However - in commercial plant operations the range is somewhat narrower ` and is typically 50 to 104 Am . Thus, fluoride acts to reduce the loss of efficiency of: sulphate based baths at low .,.
current densities. Because of the increased efficiency given to trivalent chromium plating baths the average rate of plating .-. ~ .
; 8 ~
... . . .
~?6~363~
.~ ' ' - .
.,.
from baths of the invention can be as high as 0.15 ~m min 1. Higher rates of deposition can be achieved by raising the temperature or reducing the pH.
In addition to the electrolyte described above the invention also includes a method of elec~roplating comprising providing an anode and a cathode in an electrolyte of the invention and passing an electric current through the electro-lyte whereby chromium is electrodeposited on the cathode.
The method of the invention can be carried out at a pH of from 0.5 to 7. However, in order to maintain a wide plating range-the preferred pH is from 1.5 to 4. The make-up pH of an electrolyte comprising the necessary components as a solution of the stoichiometrically neutral salts in water is usually within this range. However the pH can be readily adjusted by adding suitable small quantities of ~ acid or alkali as necessary.
-~ :
The electrolyte may be made up as in British Specification No. 1, 488,381, by a PH changing technique which can ensure formation of the desired complex between the trivalent chromium and the weak complexing agent.
!
The anodes used in the process of the invention are not critical to the process of the invention. Carbon anodes will .~ i , ~ in general be used because of their cheapness and convenience.
;'- The following Examples illustrate the invention:
, EXAMPLE 1 .; . . .
' An aqueous electrolyte having the following composition was made up:
1 M trivalent chromlum as sulphate 4 M NH4 as sulphate 0.75 M Boric Acid 1 M Sodium hypophosphite `'~
_ g_ 68t;3.9 .
Using a portion of the electrolyte a Hull Cell panel was plated under.the following conditions~
pH .- 3.1 .:
: Temperature 25C
S Hull Cell current lOA . .. . . .:
~ull Cell voltage 14V
The rësults of plating for 60 seconds were: ..
Current Density Am-2 500 1000 2000 3500 5000 -~ :
~Thick~es.s.~m 0......... 10 Ø. 11 0.1.0 0.... 11 0... 12 ~ ~
. . . , , ,,`: .
.: 10 A further portion of the electrolyte was cooled :
.. : . .. , . , ": ..
` to 10C for 12 hours and re-warmed to 25DC. A Hull Cell :. . : .
-; panel was plated under the same conditions as used above. . .
The results of plating for 60 seconds were~
.` Current.Density Am-2 500 1000 2000 3500 5000 :
lS . Thickness ~m 0.09 0.05 0.05 0.07 0.10 `~
., `~ ~s can be seen a considerable loss in plating -.
.~. : Speed occurred.
.. : , -. . .
An aqueous electrolyte having the following 20compos:ition~was made up: , ~ :
~ 1 M trivalent chromiu~ as suiphate ~.
;~ 3 M NH4~ as sulphate ::
1 M NH4~ as chloride ~;~ . 0.75 M ~oric acid 1 ~ Sodium hypophosphite . ~
' ~
.~ .
. : ' '; ~
.
.~ .
. ' .
~ . , : :, . . .. . j.... .
~068~;~9 . The electrolyte was divided into two portions : ~
and Hull Cell panels were plated-a~ set out in Example 1. :
~::
The results were: . , . .. ::;
' , .,, , ' . ' . , '`'~' '~ ',' .
Without cooling: :~
Current Density Am ~ 500 1000 2000 3500 5000 .. .
Thickness ~m 0.15 0.16 0.16 0.16 0.17 .
:, After cooling and re-warming: ~
Cuxrent Density Am~2 500 1000 2000 3500 5000 ::
. Thickness ~m 0.13 0.15 0.15- 0;15 0.15 ~: :
10 . ThP loss in plating speed after cooling and re~warming is . ~ .
. vixtually negligible. . . :.
.. ,. ., - ',' '- ~.
EX~lPLE 3 Ex~.ples l and 2 were repeated ~ut using glycine:~
, ,~... .
.. as the weak complexing agent. The observed efect of .
. 15 including chloride ion in the electrolyte was similar to .
that observed in Example 2.
~, . . .... -~ ...
` . EXA~LE 4 .
An aqueous electrolyte having the following compo~
sition was made up: . . ~. .................. .. ~. : .
... . .
1 M trivalent chromium as sulphate .~: :
3 M NH4f as sulphate . 3 M NH4~ as chloride 0.75 M Boric acid : . .. . : ..
. 1 M sodium hypophosphite ~.`
. . .
: 25 The performance of this electrolyte ~as identical to : -th~t of Example 2 except the ~lull Cell was in this case 11 volts , '"' . , -' ' , ' '. :''.
, !. ~ , - 11 - ,'. -.:,, '' . '' ''' 1061~63~
as compared to 13 volts for Example 2 indicating a ~`
superior conductivity in presence o~ higher chloride ion and ammonium ion contents.
. ':.' .
'' ' ~
EXAMPLE
An aqueous electrolyte was made up having the following composition~
1 molar trivalent chromium (as sulphate) 4 molar NH4~ (as sulphate) l molar boric acid ~:
1 molar sodium hypophosphite A Hull Cell panel was plated for 60 seconds under ,, thè following conditions: -p~ .3.0 Hull Cell current lOA
Temperature 25C Hull Cell voltage 16V `' .
The results were as follows:
/ Curxent Density (Am~2) 300 ;600 1~00 3000 5000.
`A . Thickness (~m~ 0.06 0.08 0.07 0.08 0.06 .:20 ~- .
~ EXAMPLE 6 .~ ~ Example 5 was repeated exc~pt that 6 M NH4~ ion ;~ was provided as a mixture of the sulphate t3 Mj and the . . . ~ .
chloride ~3 M). The Hull Cell panel results were: .
Current Density (Am-2) 300 500 1000 2500 5000 ; .. :.
ThicXness (~m~ 0.07 0.08 0.09 0.10 0.10 ~
- '.~
,. . ~' - ~.
~ 12 --Q76~63g ~ ; ~
-. . ~MPLE 7 ~
Example 5 was répeated except that 20 g~
(ca 0.5 M) sodium fluoride was included in the electrolyte. :`
The Hull Cell panel results were~
Current Density (Am 2) 300 500 1000 2500 5000 ~ .
Thickness (~m) 0.710 0.14 0.14.. 0.13 0.15 . There was a marked exhaltation of plating rate in .
.the presence of the fluoride.
:., .. . ' ~. ' ExAMpLE 8 Example 6 was repeated except that 20 gl~l NaF . ~
`; was included in the electrolyte. The Hull Cell panel results were: , :
Current Density (Am-2) 300 600 1000 3000 5000 .
. :
Thickness ~m) 0.12 0.14 0.15 0.14 0.14 : . Again there was a significant improvement in :
plating rate. .................................................... ~. :;.
~n a~ueous electrolyte was made up having the ollo~ing composition~
I Molar trivalent chromium (as sulphate) ..
4 ~olar NH4~ (as sulphate) `; ~ :
~.~ 1 Molax boric acid .-.
''. 7 1 Molar ~lycine ~,, ;
;~ A Elull Cell panel was plated for 60 seconds ~. ~
under the following condltion: : ~ .
p~ 2.8 ~ull Cell current 10A
:. . Temp. 25C Hull Cell voltage 16V
` 30 Th.e results were as follows~
:; Current Density (Am 2) 300 600 1000 2500 4500 ;
. Thickness (~m) 0.02 0.08 0.10 0.14 0016 - 13 - :.
, -, , .: , .,: . .. .
:` 10{;8639 ~ .
. EXAMPLE l~
Example 9 was repeated except that the 4 ~ NH
ion was provided as a mixture of the sulphate ~3 M) and the chloride (1 M) and that 20 gl 1 NaF was included. The results were as follows~
Çurrent Density (Am 2) 300 500 1000 2500 5000 .Thickness (~m) 0.05 0.10 0.11 0.15 0.16 EXAMPLE ll `lO The following aqueous electrolyte was made up: :-: l Molar trivalent chromium (as sulphate) .
3 Molar NH~+ ~as sulphate) --l Molar NH4~ (as chloride) l ~olar ~oric acid 0O5 Molar glycine 0.6 M sodium hypophosphite i;
20 g/l sodium fluoride !
A Hull Cell panel was plated for 60 seconds under the following c~nditions: l, `
. p~ 2.75 . Hull Cell current lOA - :
Temp. 26C Hull Cell voltage lOV.
: ~he results were as follo:rs:
; ' '' ' .:
.
.
;': ' .
:, ~; ~ 106~3639 Current Density (Am 2) 300 sno lO9O 2500 5000 ~ -Thickness (~m) 0.07 0.12 0.12 0.16 0~15 -.. . . . . .
EX~AMPLE 12 .. ... . .
Chromium was plated from a solution comprised `~
of~
Chrome tan 260 g/l .~ ~mmonium sulphate 180 ~
Ammonium chloride 15~ g/l Sodium flua~i~e 15 g~
Boric acid 40 g/l Sodium hypophosphite 100 g/l This solution showed good Hull Cell characteristics ~, ~ and was ultimately shown to work well on the gallon and sixty gallon sc~le~. The color of the chromium dep~sit~was slightly darker than that achieved~with conventional hexavalent chromium ;~
solutions but gave the impression of increased color depth and ~ ;
was~consid~ered to be attractlve.
The throwing power was significàntly improved and ~`
20 ~ high current density burning was substantially eliminated ~ -since the plating~rate was more or less constant regardless of the c~rrent density applied.
: ' ;:: ` i,' . .. . .
. ~
! , :
- ~, -, ' ' ~, , ,'.'. ' r . ~
~ 15 - v
Claims (23)
1. A trivalent chromium plating solution comprising water, trivalent chromium ions, sulphate ion, a weak complexing agent for said trivalent chromium ions, and halogen ions selected from the group consisting of fluoride ions, chloride ions and mixtures thereof.
2. A trivalent chromium plating solution comprising water, trivalent chromium ions, sulphate ions, a weak complexing agent for said trivalent chromium ions, and chloride ions.
3. A trivalent chromium plating solution according to claim 2 wherein the weak complexing agent is at least one of the group selected from hypophospite ions and glycine.
4. A trivalent chromium plating solution according to claim 2 containing trivalent chromium ions in a concentration of at least 0.2 M, sulphate ions in a concentration of from 1 to 6 M, a complexing agent in a concentration of at least 0.1 M, and chloride ions in a concentration of from 0.1 M to 5.0 M, the molar ratio of chloride ions to sulphate ions being from 1:60 to 5:1.
5. A trivalent chromium plating solution according to claim 4 wherein the weak complexing agent is in a concentration of from 0.25 to 3 M.
6. A trivalent chromium plating solution according to claim 4 containing ammonium ions in a concentration of from 1 to 7 M.
7. A trivalent chromium plating solution according to claim 6 containing ammonium ions in a concentration of at least 5 M.
8. A trivalent chromium plating solution according to claim 4 which contains additionally boric acid.
9. A method for electrodepositing chromium on a substrate which comprises immersing said substrate as the cathode in an electrolyte solution comprising water, trivalent chromium ions in a concentration of at least 0.2 M, sulphate ions in a concentration of from 1 to 6 M, a weak complexing agent in a concentration of at least 0.1 M, and chloride ions in a concentration of from 0.1 M to 5.0 M, and passing an electric current through said solution thereby to. deposit said trivalent chromium ions on said substrate.
10. A method or electrodepositing chromium according to claim 9 wherein the weak complexing agent is at least one of the group selected from hypophospnite ions and glycine.
11. A trivalent chromium plating solution com-prising water, trivalent chromium ions, sulphate ions, a weak complexing agent for said trivalent chromium ions, and fluoride ions.
12. A trivalent chromium plating solution according to claim 11 wherein the weak complexing agent is at least one of the group selected from hypophosphite ions and glycine.
13. A trivalent chromium plating solution according to claim 12 containing trivalent chromium ions in a concentration of at least 0.2 M, sulphate ions in a concentration of at least 0.3 M, a weak complexing agent in a concentration of at least 0.1 M, and fluoride ions in a concentration of at least 0.025 M.
14. A trivalent chromium plating solution according to claim 13 wherein the weak complexing agent is in a concentration of from 0.25 to 3 M.
15. A trivalent chromium plating solution according to claim 13 containing ammonium ions in a concentration of from 1 to 7 M.
16. A trivalent chromium plating solution according to claim 15 containing ammonium ions of at least 5 M.
17. A trivalent chromium plating solution according to claim 13 which contains additionally boric acid.
18. A trivalent chromium plating solution according to claim 13 which contains additionally chloride ions.
19. A trivalent chromium plating solution according to claim 18 which contains chloride ions in a concentration of from 0.1 to 5 M.
20. A trivalent chromium plating solution according to claim 19 containing chloride ions in a concentration of from 0.5 to 5 M, the molar ratio of chloride to sulphate being from 1:60 to 5:1.
21. A method for electrodepositing chromium on a substrate which comprises immersing said substrate as the cathode in an electrolyte solution comprising water, trivalent chromium ions in a concentration of at least 0.2 M, sulphate ions in a concentration of from 1 to 6 M, a weak complexing agent in a concentration of at least 0.1 M, and fluoride ions in a concentration of at least 0.025 M, and passing an electric current through said solution thereby to deposit said trivalent chromium ions on said substrate.
22. A method for electrodepositing chromium on a substrate according to claim 21 wherein the weak complexing agent is at least one of the group selected from hypophosphite ions and glycine.
23. A method for electrodepositing chromium on a substrate according to claim 22 wherein said solu-tion contains additionally chloride ions in a concentra-tion of from 0.1 to 5 M.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB12774/75A GB1498532A (en) | 1975-03-26 | 1975-03-26 | Trivalent chromium plating baths |
| GB1277675A GB1498533A (en) | 1975-03-26 | 1975-03-26 | Trivalent chromium plating baths |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1068639A true CA1068639A (en) | 1979-12-25 |
Family
ID=26249251
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA248,761A Expired CA1068639A (en) | 1975-03-26 | 1976-03-25 | Trivalent chromium plating baths |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1068639A (en) |
-
1976
- 1976-03-25 CA CA248,761A patent/CA1068639A/en not_active Expired
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